Mid-to-upper class socioeconomic culture slang. -aish can be inserted into any word ending in -ation, (ie presentation) to quickly convert it into slang. Usually, once it is used, the next response will also contain an -aish word, and so on.

Originated in Chicopee, Massachusetts.

Kid 1- "Hey did you go to the library to work on your presentaish?"
Kid 2- "Nah, just a little study-room masturbaish."
Kid 1-"Nice man. I gotta go to my Biochem recitaish. And wash your hands, btw."